1. Field
The present invention relates to methods and compositions for preventing, treating, and/or ameliorating fungal diseases and/or nematodes in plants via application to plant roots, seed, and/or soil of at least one pyridinyl ethylbenzamide derivative.
2. Description of Related Art
Sudden death syndrome (SDS) of soybean (Glycine max) is one of the most economically devastating plant diseases in the United States. It is among the top yield-destroying soybean diseases, with average losses exceeding $190 million per year. Yield losses are commonly between 20% and 50%, and yield losses of 100% have been reported in heavily-infested areas.
First discovered in Arkansas in 1971, SDS has been reported throughout most of the north central United States, including Illinois, Indiana, Iowa, Kansas, Kentucky, Minnesota, Mississippi, Missouri, Nebraska, Ohio, and Tennessee. SDS has also been reported in Canada, Argentina, and Brazil, for example. The disease appears to be most severe when soybeans are planted early into cool, wet soils and when heavy mid-summer rains saturate the soil.
In North America, SDS is reportedly caused by the soilborne fungus Fusarium solani f. sp. glycines, also known as Fusarium virguliforme, while in South America SDS appears to be caused by Fusarium tucumaniae. Although the pathogen colonizes soybean roots, causing root rot and vascular discoloration of roots and stems, the most evident early symptoms of SDS include mottling and mosaic of the leaves. Later, intraveinal chlorosis and/or necrosis (yellow and/or brown spots, respectively, on leaves) develops, followed by sudden leaf drop with retention of petioles (leaf stalks). The pathogen has been isolated from soybean roots and lower stems, but not leaves. The foliar symptoms are believed to be caused by fungal toxins produced on or within infected roots, which are then transported to the leaves.
Current SDS management options are limited. Although soybean varieties less sensitive to SDS have been developed, there are no highly resistant varieties; soybean breeders are developing SDS-resistant varieties, but progress has been slow. To date, fungicides applied in furrow during planting or as seed treatments have shown only limited effects. Attempts to apply fungicides to foliage have no effect on SDS, presumably because the fungal infection is restricted to root systems and fungicides typically do not move downward in the plant to reach the site of infection.
When symptoms first appear in a field, they may be localized to a few small areas—often those that are wet or compacted, such as turn rows. Symptomatic areas may expand over the subsequent weeks, and non-adjacent areas in the field may also exhibit symptoms. Because the Fusarium fungus can overwinter in soil, areas of a field that show symptoms of the disease often grow larger with each growing season.
Also, corn (maize) may be a host for the Fusarium pathogen, as it reportedly survives on corn kernels and other corn debris. Severe SDS has been reported in corn/soybean rotation fields where no SDS was observed previously. Presumably, Fusarium survives the winter as chlamydospores in the crop residue or freely in the soil. Chlamydospores can withstand wide soil temperature fluctuations (including freezing) and resist desiccation. As soil temperatures rise in the spring, chlamydospores near soybean roots are stimulated to germinate, then infect soybean roots.
There appear to be several factors that influence the spread and the severity of SDS. One of those factors is soybean cyst nematode (SCN). Fusarium virguliforme has been found inside SCN cysts, leading to speculation that these two agents both contribute to SDS symptoms. While SDS has been observed in the absence of SCN, damage due to SDS is much greater in susceptible soybean varieties when both pathogens are present than when either pathogen is present alone.
Without wishing to be bound by theory, other factors that contribute to SDS may include: susceptibility of particular soybean varieties; cool, damp conditions; early planting time; seed quality; soil compaction; and genetic diversity within the Fusarium virguliforme genome itself.
Despite wide recognition of this problem, available treatments have little to no impact on SDS; the solution is provided by the embodiments characterized in the claims.